TMessageHandler
Handle messages that might be generated by the system.
By default a handler only keeps track of the different messages
generated for a specific class. By deriving from this class and
overriding Notify() one can implement custom message handling.
In Notify() one has access to the message id and the object
generating the message. One can install more than one message
handler per class. A message handler can be removed or again
added when needed.
All Root "Warnings" are logged as message 1001
All Root "Errors" are logged as message 1002
All Root "SysErrors" are logged as message 1003
All Root "Fatals" are logged as message 1004